Order-Disorder Transition of Symmetric Poly(styrene-b-2-vinylpyridine) in Bulk and Solution

Abstract

ABSTRACT:Order-disorder transitions (ODT) of symmetric poly(styrene-b-2-vinylpyridine) in a common good solvent and bulk were determined by dynamic rheological and small-angle neutron scattering measurements. ODT conditions determined by both methods are consistent with each other and the degree of polymerization dependence of critical volume fraction in solution at almost constant temperature agrees with the theoretical prediction for semidilute solutions. However, semidilute behavior persists to a much higher concentration than for ordinary polymer solutions and the crossover from semidilute to concentrated regimes is not clear. KEY WORDSOrder-Disorder Transition / Symmetric Diblock Copolymers / Poly(styrene-b-2-vinylpyridine) / Small-Angle Neutron Scattering/ Semidilute Region/ Block copolymers exhibit a phase transition between ordered (microphase-separated) and disordered (homogeneous) states under certain conditions. The orderdisorder transitions (ODT) of block copolymers have been extensively studied and the results are summarized in the literature. 1 -8 A brief outline of the results is as follows.Theoretically, the phase diagram for diblock copolymers in bulk was first discussed by the mean-field approach,9 and later modified to include fluctuation effects. 10 According to the theory, the ODT of symmetric diblock copolymers occurs at (xN)ooT= 10.5 +41.0. N-113 ( 1) where x is the Flory-Huggins interaction parameter, N is the number of statistical segments (monomers) per copolymer molecule and (2) is a term for fluctuation correction. Here (S 2 ), Mm p, and NA are the mean square radius of gyration, number-average molecular weight, mass density and Avogadro's number, respectively. It was also predicted that eq 1 and 2 can be applied to block copolymer solutions by appropriate replacement of the parameters. 11 • 12 Experimentally, most studies on ODT have been carried out for polystyrene-polydiene diblock copolymers such as poly(styrene-b-isoprene) (SI) and hydrocarbon diblock copolymers such as poly(ethylenepropylene-b-ethylethylene) in bulk. Several experimental methods to determine ODT have been examined. At present, small-angle X-ray scattering, small-angle neutron scattering (SANS), birefringence measurement and dynamic rheological measurements (DRM) are generally used. 1 -s Recently, we studied the viscoelastic properties of SI diblock copolymer solutions near ODT and reported that t To whom correspondence should be addressed. 388the shear rate dependence of the first normal stress difference changes from first order to second order, after shear-induced alignment of the microdomain structure occurs. 13 Generally speaking, systematic studies on viscoelastic properties, especially those under steady shear flow are much easier in solution than in bulk. Difference in viscoelastic properties of block components may affect the shear-induced alignment. For better understanding of the viscoelastic properties and shearinduced alignment of diblock copolymers near ODT, it is essential to study them both ...

Phase Behavior of a Block Copolymer in Solvents of Varying Selectivity

“…Figure 1 also displays the concentration scaling of the styrene-isoprene interaction parameter, , at the OOT and ODT, as determined previously, 9 using the following expression (based on the styrene segment volume) determined from extensive results on lamellar-forming SI solutions and melts: 7 The solid line through the G 1 f C 1 OOTs follows the dilution approximation, i.e., OOT ∼ φ -1 , whereas the ODTs display the stronger dependence of ODT ∼ φ -1.4 , similar to the scaling of φ -1.6 found previously for lamellar diblocks in neutral good solvents. 7,8 For comparison, the predicted dilution approximation 7 scaling of the ODT is shown as the dashed line extending down from the melt T ODT . It overestimates T ODT by as much as 60°C at φ ) 0.55.…”

Viscoelastic Properties of Low Molecular Weight Symmetric Poly(styrene-<i>b</i>-2-vinylpyridine)s in the Ordered and Disordered States under Steady Shear Flow

“…29) Since T ODT for other M w samples cannot be determined by DMA, we determined temperature, T, dependence of χ parameter by SANS measurement using the same deutrated sample DP17 (M n : 1.2×10 4 , M w /M n : 1.05) in a much wider T range than in the previous work. 29) Using the T dependence of χ, ODT of other samples are estimated. Then the states of a few samples are confirmed by small angle X-ray scattering (SAXS) measurements at selected T s.…”

“…In a previous paper 29) , we reported that shear rate, To compare viscoelastic properties of diblock copolymers and component homopolymers, the behaviors of symmetric poly(styrene-block-2-vinylpyridine)s (SP)s, having almost the same components' viscoelastic properties 32) as well as other physical properties [33][34][35] , are studied under the dynamic and steady shear flow in a common good solvent near the ODT. [29][30][31] Corresponding structural changes under the flow are examined by small angle neutron scattering (SANS) using deutrated SP (DP).…”

“…[29][30][31] Corresponding structural changes under the flow are examined by small angle neutron scattering (SANS) using deutrated SP (DP). 30,31,[36][37][38] In the disordered states 30) , no fluctuation effect was observed on G" and shear stress σ so that the η 0 values obtained by dynamic and steady flow measurements are practically the same as those for components' solutions.…”

“…32,39) To further examine the viscoelastic properties of block copolymers, it is very interesting and essential to study SP diblocks in comparison with components for more wider range of χN in melt states, where stronger fluctuation effects are expected as shown by a previous study. 29) In this study, we examine viscoelastic properties of ordered and disordered symmetric SP diblocks having relatively low molecular weights at melt under steady shear flow based on the temperature dependence of χ obtained for the same DP sample in the previous study 29) in a wider range of temperature.…”